1. Field of the Invention
The present invention relates to a sheet processing apparatus, more particularly, a sheet processing apparatus which is designed so that sheets having been ejected from a copying machine or the like can be bound after being distributed among a plurality of bins.
2. Description of the Prior Art
Recently, responding to the increasing demand for automatized paper handling system for the copying machines, the optional systems such as the automatic document feeding system and the sorting system designed for sorting or grouping the duplicate sheets have been developed and commercialized in various types one after another. The users of the copying machines are now requiring the sorter-finisher system capable of automatically binding and stacking the duplicate sheets which have been distributed and stocked in the sorting system, and this type sorter-finisher system has already been commercialized for some of large-sized copying machines.
For example, those publicized in U.S. Pat. No. 3,944,207, issued Mar. 16, 1976 to Bains, U.S. Pat. No. 4,549,804, issued Oct. 29, 1985 to Braun et al., U.S. Pat. No. 4,248,525, issued Feb. 3, 1981 to Sterret, U.S. Pat. No. 4,361,393, issued Nov. 30, 1982 to Noto, are known as the sorter-finisher system falling under said category.
However, all such sorter-finisher systems, having a finisher wherein the sorting unit and the stapling unit are controlled in conjunction with each other, is not only unable to respond to the requirement of independently using the stapling function but also has a problem in that the sheets being processed are prevented from being stapled when other sheets are inserted into the staple tray during processing. Additionally, even when the stapling unit is made capable of independently operating, if any sheets are inserted into the staple tray by mistake, there is a possibility that the inserted sheets will be unconditionally stapled.